1. Field of the Invention
This invention relates to an electromagnetic actuator for an actuating head of a motor vehicle starter, also referred to as a starter contactor.
2. Description of Related Art
More particularly, the invention relates to a contactor for a starter of a combustion engine, especially for a motor vehicle, of the type comprising an annular coil which surrounds a cylindrical magnetic core mounted for axial sliding movement in a bore of the coil, of the type in which a rear portion of the movable core projects axially outside the fixed coil, of the type in which an external return spring for the movable magnetic core is in axial engagement against an external radial flange carried by the rear portion of the movable magnetic core and the body of the coil, of the type in which the movable magnetic core has an internal bore which is open at its rear end and which enables a coupling rod to pass through, the rear end of the coupling rod being coupled to a lever for actuating the actuator pinion which is urged elastically towards the front of the bore by an internal spring mounted in axial compression and engaged between a front shoulder surface of the coupling rod and a rear shoulder surface of the movable magnetic core, and which is arranged to engage on a base element at the front of the bore so as to be driven in straight line movement by the movable magnetic core of the starter.
In a known way, the magnetic field created by the electrical conductor wound around the body of the coil of a contactor follows lines of force which are substantially axial within the coil, and which are in the form of loops closed on themselves outside the coil.
In accordance with a known design, the movable magnetic core is generally a piece of soft iron which, whatever may be its axial position in the bore of the coil, ensures continuity of passage for magnetic flux between the carcass and the movable magnetic core. Thus, the lines of force are closed on themselves in the immediate vicinity of the coil, which enables the output of the electromagnet to be increased and the electric power consumed by the latter to be reduced.
Conventionally, the movable magnetic core is formed by a turning operation, because it has complex forms such as a rear shoulder surface of the bore of the movable magnetic core, formed internally and providing an abutment for the internal spring of the control rod, or such as a front surface formed at the base of the bore of the movable magnetic core and arranged to receive a front plate, which closes off the bore of the movable magnetic core after the components have been assembled within the bore.
This type of manufacture renders the component costly in the context of high quantity production.
In a known design, it has previously been proposed to apply to the rear face of the movable magnetic core a capping piece which includes an external flange, which is attached in such a way as to simplify the profiles of the movable magnetic core. This design, although it does partly simplify the movable magnetic core, does however not enable the rear shoulder surface of the bore of the movable magnetic core and the front surface which is to receive the closure plate to be made by any method other than by a turning operation, and the manufacture of the movable magnetic core remains expensive, the external flange not having a form which can be made by turning, so that it must be, and preferably is, an attached component.